Treatment of sea water using electrodialysis: Current efficiency evaluation

In this paper, desalination of seawater using a laboratory scale electrodialysis (ED) cell was investigated. At steady state operation of ED, the outlet concentration of dilute stream was measured at different voltages (2−6 V), flow rates (0.1−5.0 mL/s) and feed concentrations (5000−30,000 ppm). The electrical resistance of sea water solution in the dilute compartment was initially calculated using basic electrochemistry rules and average concentration of feed and dilute streams. Then, current intensity in each run was evaluated using Ohm's law. Finally, current efficiency (CE) which is an important parameter in determining the optimum range of applicability of an ED cell was calculated. It was found out that, at flow rates larger than 1.5 mL/s, higher feed concentrations lead to larger values of CE. However, exactly opposite behavior was observed at lower flow rates. Increasing the feed flow rate increases CE to a maximum value then decreases it down to zero for all cell voltages and feed concentrations. In the case of higher feed concentrations, maximum values of CE are obtained at higher flow rates. As expected, in almost all experiments, CE increases by intensifying cell voltage. CE values of up to 48 indicate effective ion transfer across the ion exchange membranes in spite of low separation performance of the ED cell.